"[16]
Coming now to a higher group--the Sea-Anemones--Mr. P.H. Gosse and other
writers on these creatures often refer to variations in size, in the
thickness and length of the tentacles, the form of the disc and of the
mouth, and the character of surface of the column, while the colour
varies enormously in a great number of the species. Similar variations
occur in all the various groups of marine invertebrata, and in the great
sub-kingdom of the mollusca they are especially numerous. Thus, Dr. S.P.
Woodward states that many present a most perplexing amount of variation,
resulting (as he supposes) from supply of food, variety of depth and of
saltness of the water; but we know that many variations are quite
independent of such causes, and we will now consider a few cases among
the land-mollusca in which they have been more carefully studied.
In the small forest region of Oahu, one of the Sandwich Islands, there
have been found about 175 species of land-shells represented by 700 or
800 varieties; and we are told by the Rev. J.T. Gulick, who studied them
carefully, that "we frequently find a genus represented in several
successive valleys by allied species, sometimes feeding on the same,
sometimes on different plants.
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